Manufacturing wet process cement



1951 o. G. LELLEP MANUFACTURING WET PROCESS CEMENT Filed Feb. 28, 19472pm mu k fwn W 2 6 M 5 0 W 0 at M.

Patented Dec. 25, 1951 ES ENT OF FTC E WET: PRO CESS CEMENT ottoGeorgezLellep, Berkeley, Cali. 7 V 'ApplicationFEbrua-ry 28, 1947,Serial No, 731,505 v .1 This invention relates :toithe ethod-p'f, andapparatus for, manufacturing wet process icement. The principalvohiectlof the invention is to lower the amount-of i uelzior burninginaradical-way. 1

As (compared with the-cry cement manufacturing method, the: wet processhas the .sadvanrtages ithatia more satisfactory mixture of the rawmaterials can he :made and :a .more constant composition can maintained,moreover that grinding of wet material re ui-res less power and theoutput of the mills is greater, and also the clinker :oi "the wetiprocess is more, easily ground; hesides, there .is less dust-connectedwith the wet process than with the dry process. There is, however, thedisadvantage that much more fuel is required to burn a slurry than:needed for binning-a dry mixture. This inventionremediesthat-iiisadvantaec'without in the least detractingiiromtheadmitted-advantagescf the wet process. At present the heatconsumption of the wet process fluctuatesvaround11,300,000 B. t. u.poi-barrel (bbli), myinventionsiorm- .ing the subject matterof-v-priorpatentsnum-bered 1,775,313, ;'1;9.92,704 and 11,994,7138, of which arerelated to the dry process, I succeeded inconsiderably increasing thefuel economy of that process, reducing th heat consumption to about700,0003. t. .11. per :b-bl. present invention enables the wet processto-be carried out with heat requirements that are but slightly higherthan those attained with ithedry process by the fuel saving.arrangements according to my previousinventions. The present inventionwill reduce the heat consumption for the wet process for instance to7-7Q;000 B. .t. u. perbbl.

It constitutes :the essence of my inventions described and claimed inthesaid prior patents that the finely divided mix of the pulverulent rawmaterials is sprayed-with water while the mix is constantly turned-overin a rotating drumduring the sprinkling operation, and thus caused toform small agglomer-ates of pea orbean size, which are; :then dried andpreburned on a gas permeable grate orthe like vbycausing rhot wastegases to pass through a pnogressinglayer of the agglomerated material,and are subsequently introduced into a kiln, e'. g. a rotaryfurnace, for

final hurnmg; preferably the waste gasesof the kiln are used for, :drymgand preburning the agglomerates upon a traveling carrier; For thepurpose of rendering: that fuel saving principle applicable to themanufacture of wet process cement, thefluidraw mix, called slurry, as itleaves the grinders of the wet process hasfirst to bev 4 claims. (01.act-#531 converted into a breakable cake; It is custom ary to partiallydewa'ter said fluid sln-rry by passing it over continuous typevacuum-filters which deliver a cake with a water content of fromiabout 19 to 2 2 percent or even more. Such a cake has .a pasty consistency likethin putty and can not be l'brokeninto non-collapsihle zfragments whichare capable-10f iformin aigas pervious layer of a thickness surpassing.many times the thickness of the single fragment;

For an eflicientheat transmission Efrem-hot kiln exit gas to the layerof rawmixturecaggregate on the grate it is essentiail that this layer heof uniform thickness and 'uniformgas permeaioility, so that all thewaste gas could pass through that layer with a suitable pressure It hasbeen suggested to take off the usual pasty, sticky filtercake from thefilter and predry it in separate drying equipment as a sheet ofcake or athin layer of cake, for instance of the same thickness as the cake. Thissuggestion to be realized requires additional-predrying equipment andheat 'which'are costly.

On a conventional filter therproduc't of partial:- 1y dewatered cementslurry is a pasty filtercake. A further removal of water is limited dueto the fact that the cake of most cement materials cracks when itisadewatered from 19"to 2-2 percent w-ater'content; Acrackingofthecakecauses loss of vacuum; and dewatering stops.

The conventional filtercake' of cement rawis too wet, pasty andcollapsible to form a thick gas permeable layer on the grate for myprevious invention. Predrying of the nasty cake inan admethods whichproduce not the usual pasty'cake,

but .a breakable cake which in fragmented state can be charged directlyin thick layer on the grate of my invention 1,992,704. This can heeffected by: compressing or compacting the filtercake stratum, or bysubjecting it to agitation; or vibration, or to the action of abe'ating' device during, or between dewateringsoperations. These methodsprevent a premature .cracldng of most cakes, produce a denser, rigidcake which has awater content of between-about 14- andl20% instead ofthe conventional water content from 1:9 to 22 or higher; Such speciallydewatered cake is rigid enough to be broken into a noncollapsible,almost nonsticky fragments in sizes mostly between inch and one inch.

The fragments or aggregates of specially dewatered filter cake are fedor charged in a 4 to 12 inch thick layer upon the gas pervious conveyoror grate of my previous invention 1,992,704 and they replace thenodules, granules or agglomerates of the dry process. It is apparent,

therefore, that the, present invention results in further conservationof power by eliminating the nodulizer generally employed in suchprocesses, and in any event, permits reducing the size and the powerconsumption of the nodulizer when it is retained as a unit of the cementmanufacturing process as it may be desirable to do in some instances.

The present invention causes a fuel saving of about 40% in wet process.Most of the raw cement slurries are adapted for being treated accordingto the method described. There are,

however, slurries which can not be filtered ecotion with the vacuumfilter drum.

I indicates a drum like vacuum filter which is supported for rotation, 2is a tank or vessel below the filter drum which receives fluid slurry ofraw cement mixture. The drum may be rotated in any convenient manner.This filter is equipped with means for compacting the filter cake bedformed, for instance with compression rolls 3. In the construction shownin Fig. 1,

these compression rolls 3 exercise a pressure on the filter cake bedthrough an absorbent compression belt 4, which is moved by the filtersurface and carried by guiding rolls 5. The rolls 3 and 5 are fixed to asupporting member 6, this compression mechanism prevents prematurecracking'of the filter cake bed formed on the surface of the drum and aconsequent loss of vacuum.

Other means and methods known of themselves may be applied to arrive atcompacting the filter cake bed during or between the vacuum 'dewateringoperations, and thus to obtain a filter cake with unusually low watercontent. The

cake may for instance be agitated with pulsat- -ing air introduced intothe vacuum system, or by the action of a vibrating roller on the surfaceof the cake. A somewhat similar effect is attainable by slapping thecake with pieces of belting 44 fixed to a rotation shaft 45 that isarranged above the travelling filter cake bed.

In whatever manner the compacting of the filter cake bed may be broughtabout, the filter .cake should be suificiently rigid when it arrives atthe discharging point, where, as shown in the drawings, a scraper 1 isprovided for removing the filter cake stratum from the surface of thedrum and supplying the material to a crusher or breaker 8, the fragmentsproduced gliding over a chute 9 into a bin H1.

According to the construction shown in Fig. 1,

,the filter cake fragments are then distributed in -layer vl3 on a gaspermeable travelling carrier l I,

e. g. a conveyor belt, which is carried and moved 4 consecutivelythrough a drying system 14 and a preburning system I5 which areseparated through wall 29 above the conveyor belt and by wall 30 belowthe conveyor belt, in which latter wall there is an opening 3| with aregulating damper 22. The pretreated charge is then caused to pass overa chute 16 into a rotary kiln H, where it is calcined and eventuallyconveyed into a clinkering zone kept at white heat which is supplied byburner 18. From the lower end of the rotary kiln clinker falls intotheclinker cooler [3, where it is cooled by air which is supplied bymotorized propeller fan 20.

The main part of heat on the grate II is derived from the exit gas ofthe rotary kiln I! that fills the chamber l5. In the preburning system,

( this gas which isin a temperature range around ing into channel 24that is equally equipped with a damper 22. Surplus warm air is directedfrom clinker cooler l3 through duct 25, to join with the hot air comingthrough channel 24, and the mixture is moved by fan 26 through duct 21to join with the hot gas issuing from channel 2| and flowing into thedrying system [4 through channel 28. In the drying chamber the gas whichis moved by the fan draft passes through layer [3 and gratell. The exitgases of both the drying and preburning systems are conducted toatmosphere through fan opening 34, the flow of the hot'gases beingeffected by the fan draft and the whole gas circulation being adjustedby the respective dampers 22, in such a manner that the temperatureabove the drying grate is kept at approximately 300 C.

The construction shown in Fig. 2 essentially differs from thatillustrated in Fig. 1 only in the detail that the drying and preburningsystems are separated from each other, the preburnin'g system beingdirectly heated by the exit gases of the rotary kiln while the dryingsystem receives the exit gases issuing from the preburning system. Thetraveling carrier ll moving through the drying system discharges thedried filter cake fragments into a large bin 10, from where they are fedupon another gas permeable carrier 32 arranged to move through aseparate'preburning system. The exit gas from this system is movedthrough layer I3 by fan 33 into channel 36 from where it flows into thedrying chamber M.

A branch line 21 with damper 22 is provided for a supply of additionalhot air heat derived from the lower end'of the rotary kiln as shown onFig. 1. In case in doing so a too high temperature for drying would beproduced, atmospheric air is' simultaneously introduced into channel 36to keep the-drying gas temperature around 300 C. The arrangement on Fig.2 allows a better heat utilization than on Fig. 1. Bin l0 between thetwo grates in Fig. 2 has a large capacity for dried cake which serves asreserve feed for the preheating grate and the kiln in case the filter isstopped temporarily for repairs or servicing.

The main feature of this invention is the cornbination of steps in whichthe wet process raw mixture slurry is dewatered by mechanical means byrollers 12, said carrier being arranged to pass 15 in contrast tothermal from the state of past into pacted during the filtrationprocess.

be produced also by a filter of multiple disc type of larger capacity ifthe cake on this filter is com- A low water, rigid, and breakable cakeproduced by a disc filter can be formed into suitable, small aggregatesof any shape like slugs, pills, briquettes, sausages, by using a pugmill or a press. A layer of such aggregates can be charged directly uponthe grate of my invention 1,992,704.

I claim:

1. An apparatus for manufacturing wet process cement comprising a rotarykiln having a pretreatment apparatus into which the hot exhaust gasesfrom the kiln are delivered, in combination with a filter drum having apervious wall, means for establishing a reduced pressure at the interior2 surface .of the said pervious wall, means for delivering cement slurryto the exterior surface of said pervious wall, a compacting meansdisposed immediately above the exterior surface of said pervious walland positioned to compress material carried on the said exteriorsurface, and delivery means operably associated with said exteriorsurface and compacting means for receiving material from said exteriorsurface and delivering the material to the said pretreatment apparatus.

2. An apparatus as claimed in claim 1 in which said compacting meanscomprises cylindrical rolls freely supported on shafts mounted inparallelism with the axis of said drum.

3. An apparatus as claimed in claim 2 in which said compacting meanscomprises an endless belt passing around said cylindrical rolls betweenthe said rolls and the exterior surface of said pervious Wall.

4. An apparatus for manufacturing wet process cement comprising a rotarykiln having a pretreatment apparatus into which the hot exhaust gasesfrom the kiln are delivered, in combination with a filter drum having apervious wall, means for establishing a reduced pressure at the interiorsurface of said pervious wall, means for delivering cement slurry to theexterior surface of said pervious wall, a compacting means comprising arotary shaft having a flexible plate fixed thereto and extendingradially therefrom disposed immediately above the exterior surface ofsaid pervious wall and positioned to compress material carried on thesaid exterior surface, and delivery means operably associated with saidexterior surface and compacting means for receiving material from saidexterior surface and delivering the material to the said pre-treatmentapparatus.

OTTO GEORGE LELLEP.

REFERENCES CITED The following references are of record in the file ofthis patent: 3

UNITED STATES PATENTS Andrews Aug. 10, 1943

